[PATCH v18 4/8] ring-buffer: Skip invalid sub-buffers when rewinding persistent ring buffer

[Steven Rostedt]

On Thu, 30 Apr 2026 00:20:23 +0900
Masami Hiramatsu (Google) <mhiramat at kernel.org> wrote:

> On Tue, 28 Apr 2026 16:21:46 -0400
> Steven Rostedt <rostedt at goodmis.org> wrote:
> 
> > On Fri, 24 Apr 2026 15:52:35 +0900
> > "Masami Hiramatsu (Google)" <mhiramat at kernel.org> wrote:
> >   
> > > @@ -1892,9 +1895,19 @@ static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu,
> > >  	 * subbuf_size is considered invalid.
> > >  	 */
> > >  	tail = local_read(&dpage->commit) & ~RB_MISSED_MASK;
> > > -	if (tail > meta->subbuf_size - BUF_PAGE_HDR_SIZE)
> > > -		return -1;
> > > -	return rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
> > > +	if (tail <= meta->subbuf_size - BUF_PAGE_HDR_SIZE)
> > > +		ret = rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
> > > +  
> > 
> > This code seriously needs comments.  
> 
> OK, I'll add it, or let code explain clearer?
> 
> 	if (tail <= meta->subbuf_size - BUF_PAGE_HDR_SIZE)
> 		ret = rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
> 	else
> 		ret = -1;

That's better...

> 
> Thanks,
> 

The below should have some explanation too. I can figure it out, but it
wasted more brain cycles than I would have liked ;-)

-- Steve


> >   
> > > +	if (ret < 0 || (prev_ts && prev_ts > ts) || (next_ts && ts > next_ts)) {
> > > +		local_set(&bpage->entries, 0);
> > > +		local_set(&bpage->page->commit, 0);
> > > +		bpage->page->time_stamp = prev_ts ? prev_ts : next_ts;
> > > +		ret = -1;
> > > +	} else {
> > > +		local_set(&bpage->entries, ret);
> > > +	}
> > > +
> > > +	return ret;
> > >  }
> > >    
> 
>